Among the various types of batteries available at present, lithium ion batteries are attracting attention from the viewpoint of their high energy density. In particular, all-solid-state batteries, in which the electrolytic solution has been replaced with a solid electrolyte, are attracting attention among these batteries. This is because, differing from secondary batteries using an electrolytic solution, since all-solid-state batteries do not use an electrolytic solution, there is no degradation of the electrolytic solution caused by overcharging and these batteries have high cycling characteristics and high energy density.
When an all-solid-state battery is used improperly, such as in the case of causing an external short-circuit, overcharging, heating or allowing a metal fragment or other foreign object to enter the battery during battery production, the all-solid-state battery may undergo an internal short-circuit. Therefore, research is being conducted on a technology for preventing internal short-circuiting during improper use etc., of an all-solid-state battery.
Incidentally, Patent Documents 1 and 2 disclose a technology for improving ion conductivity by mixing α-alumina having an average particle diameter of 10 μm or less with a sulfide solid electrolyte or sulfide glass solid electrolyte. In addition, Patent Document 3 discloses a solid electrolyte material for improving ion conductivity that is obtained by mixing α-alumina having an average particle diameter of 1 μm or less with a lithium halide.